@Urban Sky You're better at this. For a hypothetical HFR from Toronto to Quebec City, with hourly departures, how many trains would be needed? My very rough ballpark says 18-22.
1) Add the
travel times for TRTO-MTRL and MTRL-QBEC.
2) Add a realistic dwell time for Montreal's Gare Centrale. The minimum scheduled dwell time is currently 15 minutes (train 35, arrive 11:49, depart 12:04) and I didn't find any shorter dwell time for since VIA introduced Quebec-Montreal-Ottawa trains in December 2012.
3) Add a realistic turn-around time. VIA's fastest scheduled turn-around time between two different train services travelling in two different directions I'm aware of is 75 minutes (train 73 arrives Windsor at 16:30 and departs as train 78 at 17:45), which includes physically turning the train, whereas I've seen JR Central/East scheduling as little as 6 minutes between the arrival and departure of their (obviously bidirectional) Shinkansen trains from/to Tokyo at Kanazawa (a dead-end terminus station).
4) Multiply the result by 2 and round up to the next full hour. The resulting number of hours is the minimum number of cycles you'll need to allocate with trainsets during the day.
In order to calculate the number of physical trainsets you require, you need to also consider the following:
5) Are there any departures for which I may need two trainsets (think of the ICE-2, ICE-3 or TGV Duplex), to cope with demand?
6) How many trainsets are needed as guard trains at strategic points?
7) Take the calculated number of trainsets and add a margin for planned or unplanned vehicle unavailabilities (training, maintenance, defects, repairs, wrecks).
I hope this helps!